EKSTRASI LOGAM Sutarno
Ekstraksi bijih logam
Tahapan proses ekstrasi logam murni Penambangan mineral Peningkatan kadar bijih logam Reduksi bijih logam
Pemurnian logam
Pembuatan Paduan logam
Ekstraksi
Mining countries: China, Australia, Peru,Canada, US, Mexico, Ireland, Kazakhstan, India, Namibia, and 27 others Smelting, leaching/refining countries: China, Canada, Korea, Japan, Spain, Australia, Kazakhstan, USA, India, France and 23 others World Annual Zn production: approximately 10 million ton
Sebagaimana telah dibahas, proses yang umumnya dilakukan untuk produksi Zn dari bijih ZnS adalah Proses RLE (RoastLeach-Electrowinning)
– ZnS + 3/2O2O2 = ZnO + SO2 (roasting) – ZnO + H2SO4 = ZnSO4 + H2O (acid leaching)
ZnS dapat dilindi secara langsung dalam kondisi tertentu di dalam autoclave (pressure leaching), atau dalam tekanan atmosfer dan dengan bantuan bakteri (bacterial leaching)
Leaching (Pelindian) •
•
Proses dimana senyawa berisi logam secara selektif terpisahkan dengan melarut. Dapat mengggunakan air jika senyawa berisi logam tersebut larut dalam air, tetapi lebih sering berupa asam, basa dan larutan garam.
4 Au(s) + 8 CN (aq) + O2(g ) + 2 H2O(l ) −
4 Au(CN)2 (aq) + 4 OH −
2 Au(CN)2 (aq) + Zn(s) Zn(CN)42 (aq) + 2 Au(s) −
−
−
(aq)
Proses Bayer •
Metoda pemurnian bauxite (bijih aluminum). Al2O3 H2O(s) + 2 H2O(l ) + 2 OH (aq) 2 Al(OH)4 (aq) ∙
•
−
−
Ion aluminate dapat larut dipisahkan dari pengotor yang tidak larut (SiO 2 dan Fe3O3) dengan filtrasi (penyaringan).
Chemical method : 1. In this method the ore is treated with a suitable chemical reagent which dissolves the ore leaving behind insoluble impurities. 2. The ore is then recovered from the solution by a suitable chemical method. 3. This is applied for extraction of aluminium from bauxite Al2O3.2H2O. 4. Bauxite is contaminated with iron (III) oxide Fe2O3 , titanium (IV) oxide TiO2 and silica, SiO2 . 5. These impurities are removed by digesting the powdered ore with aqueous solution of sodium hydroxide at 420 K under pressure.
6. Aluminium oxide dissolves in sodium hydroxide, whereas, iron (III) Chemistry of Elements oxide, silica and titanium (IV) oxide remain insoluble and are removed by iltration. Al2O3 + 6NaOH 2Na3AlO3 + 3H2O Sodium aluminate Sodium aluminate is diluted with water to obtain precipitate of aluminium hydroxide. It is filtered and ignited to obtain pure alumina. Na3AlO3 + 3H2O Al(OH) 3 + 3NaOH 2Al(OH)3 Al2O3 + 3H2O
For some metals for which reduction with carbon is unsuitable, electrolysis of melts may be used. Aluminium is a good example. 1.
The raw materials for the extraction of aluminium are purified aluminium oxide (Al2O3) and cryolite (Na3AlF6).
2.
The aluminium oxide must be molten or dissolved to conduct electricity, and so is dissolved in molten cryolite (this
3.
requires a lower temperature than using molten aluminium oxide so has lower energy
costs). 4.
The electrodes are made of graphite.
5.
This is a continuous process.
Aluminum
Dalam proses Hall process, Al 2O3 terlarut dalam lelehan (Na2 AlF6), dan Al3+ direduksi menjadi Al.
cryolite
Aluminium
In the metallurgy of aluminium, purified Al2O3 is mixed with Na3AlF6 or CaF2 which lowers the melting point of the mix and brings conductivity. The fused matrix is electrolysed. Steel vessel with lining of carbon acts as cathode and graphite anode is used. The overall reaction may be written as:
2Al2O3 + 3C
→
4Al + 3CO2
(6.44)
This process of electrolysis is widely known as Hall-Heroult process. Thus electrolysis of the molten mass is carried out in an electrolytic cell using carbon electrodes. The oxygen liberated at anode reacts with the carbon of anode producing CO and CO2. This way for each kg of aluminium produced, about 0.5 kg of carbon anode is burnt away. The electrolytic reactions are: Cathode: Al3+(melt) + 3e –
→
Al(l)
Anode: C(s) + O2 – (melt) CO(g) + 2e – C(s) + 2O2 – (melt) CO2 (g) + 4e – →
→
(6.45)
(6.46) (6.47)
Electrolitic cell
